Nanostructures have been incorporated into many kinds of sensors to obtain high sensitivity and specificity. For example, in surface enhanced Raman spectroscopy (SERS) based sensors, using colloidal silver nano-particles, researchers were able to detect single dye molecules with an enhancement factor on the order of 1014-1015; in surface plasmon resonance (SPR) based sensors, silver or gold nano-particle films have been used to dynamically tune the resonance wavelength. Also, using fiber optics in SERS or SPR, one can miniaturize the device while maintaining the sensitivity. So far, there are several limited methods for preparing nanostructures on fiber optical probes suitable for SERS and SPR based sensors, for example, sputtering or e-beam evaporating metal thin films onto optical fiber tips, or dipping functionalized optical fibers into colloidal solutions. Nanostructures prepared by the dipping method are random, and the reproducibility is poor. It is also important that the fabrication technique is compatible with current microfabrication processes.